The present invention relates to a room temperature-curable organopolysiloxane composition useful as an adhesive or, more particularly, to a novel room temperature-curable organopolysiloxane composition with extended tack-free time prepared by formulation a novel organopolysiloxane component.
There are hitherto known various types of organopolysiloxane composition useful as an adhesive curable at room temperature when exposed to a moisture-containing atmosphere with the crosslink formation by virtue of a crosslinking agent formulated therein. The principle or mechanism of crosslink formation leading to curing of the composition naturally depends on the kind of the crosslinking agent. In particular, several kinds of prior art room temperature-curable organopolysiloxane compositions contain an aminoxy-containing organopolysiloxane or organosilane as the crosslinking agent. Among the room temperature-curable organopolysiloxane compositions belonging to this class, those disclosed in Japanese Patent Publication No. 42-24545 contain both of a difunctional and trifunctional aminoxysilanes as the crosslinking agents formulated with the base component which is a linear diorganopolysiloxane terminated at both molecular chain ends with silanolic hydroxy groups. A problem in the room temperature-curable composition of this type is in the storability of the ready-mixed composition. That is, the composition prepared by blending all of the components together is rapidly gelled even in a hermetically sealed condition so that the composition cannot be stored with stability as a ready-mixed premix on one package. Therefore, it is a usual practice that the composition is prepared in two packages each containing different kind or combination of the components from the other and the contents of these two packages are blended together in a suitable proportion directly before use. It may be too much to say that the ready-mixed one-package type compositions are preferred to the two-package type compositions from the standpoint of working efficiency if the problem of storability is of no matter.
In order to solve the above mentioned problem in the storability of the ready-mixed composition, there has been proposed a room temperature-curable organopolysiloxane composition capable of giving a rubbery cured product, which is formulated with a difunctional amidosilane and a tri- or tetrafunctional aminoxysilane in place of the di- and trifunctional aminoxysilanes (see, for example, Japanese Patent Publication No. 52-30020). A problem in the room temperature curable composition of this type is the poor adhesion to the substrate surface to which the composition is applied and on which it is cured due to the liberation of a high-boiling amide compound in the course of the curing reaction. A remedy for the poor adhesion may be afforded by formulating the composition with an adhesion aid such as 3-aminopropyl triethoxysilane and the like although the addition of such an adhesion aid is undesirable due to the markedly poor curing performance of the composition admixed therewith. In addition, such a composition suffers from another problem of a relatively short workable time due to surface filming ranging, for example, from 15 to 40 minutes so that the application of the composition in the fields of civil engineering or building works is limited since the composition having been applied to a substrate surface must be finished by troweling hastily within a short time before the loss of workability of the composition by surface filming.